Acute pancreatitis is a common life threatening disorder of the pancreas. Irrespective of etiology, an early step in all disease forms is the premature activation of proenzymes (zymogens) within the pancreatic acinar cell. This event depends on pathologic intracellular Ca2+ signals. Acinar cell Ca2+ release is predominantly controlled by two endoplasmic reticulum Ca2+ channels, the inositol trisphosphate receptor (IP3R) channel and the ryanodine receptor (RYR) channel. The IP3R is localized to the apical region where digestive enzymes are secreted, but not activated. In contrast, the RYR partially localizes to a supranuclear region that overlaps with the region of initial zymogen activation. Based on this observation, we hypothesize a novel function for Ca2+ released by the RYR; it primarily regulates zymogen activation, but not digestive enzyme secretion. In preliminary work, the role of the RYR in zymogen activation was examined using both an in vitro and in vivo model of pancreatitis. We found that two RYR antagonists, dantrolene and ryanodine, reduced cholecystokinin (CCK)-induced zymogen activation. Notably, these agents did not affect CCK-induced secretion. The specific aims of this project are first to determine if conditions that cause zymogen activation evoke localized RYR-mediated Ca2+ release; second to examine if localized RYR-mediated Ca2+ release causes zymogen activation; third to study the effects of inhibiting the RYR in vivo on the severity of pancreatitis using RYR antagonist therapy or gene deletion. This work will provide improved understanding of the mechanisms leading to aberrant Ca2+ signaling and zymogen activation in acute pancreatitis and may suggest a new treatment strategy that targets the RYR. The candidate is completing a fellowship at Yale University in Pediatric Gastroenterology and will continue there as junior faculty. Yale is an ideal training environment because of the infrastructure for research training in digestive diseases. In addition, the candidate will be mentored by individuals with particular expertise in pancreatitis and acinar Ca2+ signaling, and both mentors have extensive experience training fellows as well.